Micro-Electro-Mechanical Systems (MEMS) is a widely used technology that enables integration of both microelectronic circuits and mechanical structures on the same chip, while significantly lowering fabrication costs and chip size. For at least these reasons MEMS microphones are being widely used in consumer electronic devices, such as, mobile phones, tablet computers, laptops, gaming devices, etc. Typically, MEMS microphones detect a change in a capacitance of a variable capacitor having a fixed back-plate and flexible membrane. The change in capacitance is caused by a sound wave, passing through a port hole in a package substrate, that moves the membrane modulating the air gap between the membrane and the fixed back-plate.
Conventionally, the size of the port hole is kept small to protect the device from environment interference (e.g., particles, light and solder flux from a surface-mount technology process, etc.). Further, the port hole size is fixed by customers based on their board design. However, the small port hole has negative impact on microphone performance. Moreover, with smaller port holes, mass loading due to air inside front volume, formed between port hole and MEMS backside cavity, is increased, which in turn leads to a decrease in a resonant frequency, a lower resonant peak, a lower signal-to-noise ratio (SNR) and narrower range for flat frequency response of the MEMS microphone.